HD 22496 b: The first ESPRESSO stand-alone planet discovery^★,★★

¹ Centro de Astrobiología (CAB, CSIC-INTA), Departmento de Astrofísica, ESAC campus, 28692, Villanueva de la Cañada (Madrid), Spain
e-mail: jorge.lillo@cab.inta-csic.es
² Departmento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 4169-007 Porto, Portugal
³ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
⁴ Instituto de Astrofísica de Canarias (IAC), Calle Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
⁵ Departamento de Astrofísica, Universidad de La Laguna (ULL), 38206 La Laguna, Tenerife, Spain
⁶ European Southern Observatory, Alonso de Cordova 3107, Vitacura, Region Metropolitana, Chile
⁷ Centro de Astrobiología (CSIC-INTA), Crta. Ajalvir km 4, 28850 Torrejón de Ardoz, Madrid, Spain
⁸ Département d’astronomie de l’Université de Genève, Chemin Pegasi 51, 1290 Versoix, Switzerland
⁹ INAF – Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
¹⁰ INAF – Osservatorio Astrofisico di Torino, via Osservatorio 20, 10025 Pino Torinese, Italy
¹¹ Aix Marseille Univ, CNRS, CNES, LAM, Marseille, France
¹² Consejo Superior de Investigaciones Cientícas, Spain
¹³ INAF – Osservatorio Astronomico di Trieste, via G. B. Tiepolo 11, 34143 Trieste, Italy
¹⁴ Department of Physics, and Institute for Research on Exoplanets, Université de Montréal, Montréal, H3T 1J4, Canada
¹⁵ Instituto de Astrofísica e Ciências do Espaço, Faculdade de Ciências da Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal
¹⁶ Faculdade de Ciências da Universidade de Lisboa (Departamento de Física), Edifício C8, 1749-016 Lisboa, Portugal
¹⁷ Centro de Astrofísica da Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal
¹⁸ Institute for Fundamental Physics of the Universe, Via Beirut 2, 34151 Miramare, Trieste, Italy
¹⁹ ESO, Karl Schwarzschild Strasse 2, 85748, Garching bei Muenchen, Germany
²⁰ Fundación G. Galilei – INAF (Telescopio Nazionale Galileo), Rambla J. A. Fernández Pérez 7, 38712 Breña Baja, La Palma, Spain
²¹ INAF – Osservatorio Astronomico di Brera, Via E. Bianchi 46, 23807 Merate, Italy

Received: 5 July 2021
Accepted: 27 August 2021

Abstract

Context. The ESPRESSO spectrograph is a new powerful tool developed to detect and characterize extrasolar planets. Its design allows an unprecedented radial velocity precision (down to a few tens of cm s⁻¹) and long-term thermomechanical stability.

Aims. We present the first stand-alone detection of an extrasolar planet by blind radial velocity search using ESPRESSO; our aim is to show the power of the instrument in characterizing planetary signals at different periodicities in long observing time spans.

Methods. We used 41 ESPRESSO measurements of HD 22496 obtained within a time span of 895 days with a median photon noise of 18 cm s⁻¹. A radial velocity analysis was performed to test the presence of planets in the system and to account for the stellar activity of this K5-K7 main-sequence star. For benchmarking and comparison, we attempted the detection with 43 archive HARPS measurements and in this work we compare the results yielded by the two datasets. We also used four TESS sectors to search for transits.

Results. We find radial velocity variations compatible with a close-in planet with an orbital period of P = 5.09071 ± 0.00026 days when simultaneously accounting for the effects of stellar activity on longer timescales (P_rot = 34.99_−0.53^+0.58 days). We characterize the physical and orbital properties of the planet and find a minimum mass of 5.57_−0.68^+0.73 M_⊕, right in the dichotomic regime between rocky and gaseous planets. Although not transiting according to TESS data, if aligned with the stellar spin axis, the absolute mass of the planet must be below 16 M_⊕. We find no significant evidence for additional signals in the data with semi-amplitudes above 56 cm s⁻¹ at 95% confidence.

Conclusions. With a modest set of radial velocity measurements, ESPRESSO is capable of detecting and characterizing low-mass planets and constraining the presence of planets in the habitable zone of K dwarfs down to the rocky-mass regime.